How To Design RF Circuits - Synthesisers

Introduction Frequency synthesisers form the basis of most radio system designs and their performance is often key to the overall operation. This paper will present an introductory overview of the basic parameters governing the design of a phase locked loop frequency synthesiser and their effects, with the sources of phase noise within a design also being considered. Finally a list of common problems, along with some possible solutions, is giv en in order to assist in the debugging of a non-functional design once assembled. What is a Synthesiser? A synthesiser is a device which takes an input, or source, frequency and from it produces an output frequency which is either directly or indirectly related to it. Possible schemes for direct and indirect synthesisers are shown in figure 1.